We will investigate the pathological effects in mice of several zeolites by intraperitoneal injection of 10mg of four types of zeolites (2 fibrous erionites, mordenite, and non-fibrous zeolite). A single peritoneal injection will be utilized, followed by study after serial sacrifice or spontaneous death of the animals. Investigations will include gross anatomy, histology, histochemistry, and electron microscopy including transmission, scanning and high resolution analytical microscopy. Questions to be investigated include: (1) Do these zeolites induce malignant tumors? (2) If they do, are there differences in the neoplastic effects among them? (3) What kinds of malignant tumors are produced? (4) If malignant mesothelioma is produced -- a) what is the pathogenetic process in its development? b) Are these explanations for the differences, if any, in the incidence of the mesothelioma production among the four zeolites? c) Is the histogenesis of malignant mesothelioma identical or similar for zeolites and asbestos? If there are differences, what are they? d) Are there features of zeolite-induced mesothelioma to allow differentiation from those induced by asbestos? (5) Do these zeolites induce fibroplastic effects? (6) How do the fibroplastic effects among the four zeolites differ? (7) Are "hyaline plaque formation" and pseudo-asbestos ("ferruginous") body formation" seen in zeolite-induced fibrosis? (8) Is the process of the zeolite-induced fibrosis similar to that induced by asbestos? (9) Is fibrosis pathogenetically related to development of mesothelioma?